Buried object locating methods and apparatus using multiple electromagnetic signals

ABSTRACT

A method of locating buried objects using a locator having at least one antenna array including three mutually orthogonal antennas each sharing a common center point includes simultaneously determining a plurality of magnetic fields associated with a plurality of different electromagnetic signals and providing a visual indication of the determined magnetic fields on a display of the locator.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims priority to co-pendingU.S. Utility patent application Ser. No. 12/916,886, entitled METHOD FORSIMULTANEOUSLY DETERMINING A PLURALITY OF DIFFERENT LOCATIONS OF BURIEDOBJECTS AND SIMULTANEOUSLY INDICTING THE DIFFERENT LOCATIONS TO A USER,filed Nov. 1, 2010, which is a divisional application of U.S. Utilitypatent application Ser. No. 12/579,539 (now U.S. Pat. No. 7,830,149),entitled AN UNDERGROUND UTILITY LOCATOR WITH A TRANSMITTER, A PAIR OFUPWARDLY OPENING POCKETS AND HELICAL COIL TYPE ELECTRICAL CORDS, filedOct. 15, 2009, which is a divisional application of U.S. Utility patentapplication Ser. No. 11/077,947 (now U.S. Pat. No. 7,619,516), entitledSINGLE AND MULTI-TRACE OMNIDIRECTIONAL SONDE AND LINE LOCATORS ANDTRANSMITTER USED THEREWITH, filed Mar. 11, 2005, which is a divisionalapplication of U.S. Utility patent application Ser. No. 10/308,752,entitled SINGLE AND MULTI-TRACE OMNIDIRECTIONAL SONDE AND LINE LOCATORSAND TRANSMITTER FOR USE THEREWITH, filed Dec. 3, 2002, which is acontinuation-in-part application of U.S. Utility patent application Ser.No. 10/268,641 (now U.S. Pat. No. 7,009,399), entitled OMNIDIRECTIONALSONDE AND LINE LOCATOR, filed Oct. 9, 2002. This application claimspriority each of these applications, and the content of each of theseapplications is incorporated by reference herein its entirety for allpurposes.

FIELD

This disclosure relates generally to electronic devices, systems andmethods for locating buried or otherwise inaccessible pipes and otherconduits, as well as cables, conductors and inserted transmitters, bydetecting an electromagnetic signal emitted by these buried objects.

BACKGROUND

There are many situations where is it desirable to locate buriedutilities such as pipes and cables. For example, prior to starting anynew construction that involves excavation, it is important to locateexisting underground utilities such as underground power lines, gaslines, phone lines, fiber optic cable conduits, CATV cables, sprinklercontrol wiring, water pipes, sewer pipes, etc., collectively andindividually referred to herein with the term “objects.” As used hereinthe term “buried” refers not only to objects below the surface of theground, but in addition, to objects located inside walls, between floorsin multi-story buildings or cast into concrete slabs, etc. If a back hoeor other excavation equipment hits a high voltage line or a gas line,serious injury and property damage can result. Severing water mains andsewer lines leads to messy cleanups. The destruction of power and datacables can seriously disrupt the comfort and convenience of residentsand cost businesses huge financial losses.

Buried objects can be located by sensing an electromagnetic signalemitted by the same. Some cables such as power lines are alreadyenergized and emit their own long cylindrical electromagnetic field.Other conductive lines need to be energized with an outside electricalsource having a frequency typically in a range of approximately 50 Hz to500 kHz in order to be located. Location of buried long conductors isoften referred to as “line tracing.”

A sonde (also called a transmitter, beacon or duct probe) typicallyincludes a coil of wire wrapped around a ferromagnetic core. The coil isenergized with a standard electrical source at a desired frequency,typically in a range of approximately 50 Hz to 500 kHz. The sonde can beattached to a push cable or line or it may be self-contained so that itcan be flushed. A sonde generates a more complex electromagnetic fieldthan that produced by an energized line. However, a sonde can belocalized to a single point. A typical low frequency sonde does notstrongly couple to other objects and thereby produce complex interferingfields that can occur during tracing. The term “buried objects” as usedherein also includes sondes and marker balls.

Besides locating buried objects prior to excavation, it is furtherdesirable to be able to determine their depth. This is generally done bymeasuring the difference in field strength at two locations.

The prior art includes many battery powered portable sonde and linelocators that employ antennas to sense an electromagnetic signal emittedby buried objects and indicate their location via audible tones anddisplays. Those that have been commercialized have been difficult to useprimarily because they are extremely sensitive to the orientation oftheir antennas relative to the buried object. With commerciallyavailable sonde and line locators it is possible to have signal strengthgo up as the operator moves farther away from the buried object. Thusthese locators can indicate a peak, then a null and then a smaller peak.This can confuse the operator, especially if he or she interprets asmaller peak as the buried object. Users of sonde and line locatorsrefer to the smaller peak as a ghost or a false peak.

FIG. 1 is a graphical vertical sectional view that illustrates theforegoing difficulty. A sonde 10 is located inside a plastic pipe 12beneath a concrete slab 14. The electromagnetic dipole field emitted bythe sonde 10 is illustrated by concentric ovals 16. A conventionallocator will “see” two smaller false peaks 18 and 20 spaced from thetrue larger peak 22 by a pair of nulls 24 and 26.

Conventional battery powered portable sonde and line locators have alsosuffered from user interfaces that are cumbersome to use, inflexibleand/or limited in their ability to convey useful information. Theytypically have a small array of labeled push buttons and a display thatis primarily dedicated to indicating numerical values in a manner thatis not easy for the operator to interpret. Only a small number ofcommands can be executed in conventional sonde and line locators and theinformation is not displayed in a manner that intuitively indicates tothe operator how close he or she is getting to the buried object.

There are many instances where the land that is to be excavated may betraversed or crisscrossed by several different utilities such as an ACcable, a water line, a gas line, a sewer pipe and a communications line.It would be desirable to be able to determine their paths and theirdepths all at one time. Conventional transmitters are commerciallyavailable that will output several different signals at differentfrequencies that can be applied to the same underground object or evento different underground objects, but the line locators that haveheretofore been commercially available have not been capable ofsimultaneously detecting and indicating the locations of the differentobjects, their depths or their different types.

Accordingly, there is a need in the art to address the above-describedas well as other problems related to buried object identification.

SUMMARY

In accordance with one aspect, portable sondes and line locators aredisclosed.

In another aspect, an improved method for locating one or more buriedobjects by sensing electromagnetic signals emitted from the buriedobjects are disclosed.

In another aspect, portable sondes and line locators with an improvedgraphical user interface (GUI) are disclosed.

In another aspect, portable locators that can simultaneously detectdifferent buried objects and simultaneously indicate their differentlocations based on electromagnetic signals are disclosed.

In another aspect, portable locators including location identificationand/or mapping functions are disclosed.

Various additional aspects, features, and functions are furtherdescribed below in conjunction with the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure may be more fully appreciated in connection withthe following detailed description taken in conjunction with theaccompanying drawings, wherein:

FIG. 1 is a graphical vertical sectional view illustrating a prior arttechnique of locating a buried sonde.

FIG. 2 is a perspective view of a portable battery powered sonde andline locator representing a first embodiment of our invention that isdesigned to sense and display the location of a single buried object atone time.

FIG. 3 is an enlarged view of the antenna mast and two sensor balls ofthe first embodiment.

FIG. 4 is an enlarged, broken away view of the lower sensor ball of thefirst embodiment.

FIG. 5 is an enlarged, broken away view of the upper sensor ball of thefirst embodiment.

FIG. 6 is a functional block diagram of the electronic circuitry of thefirst embodiment.

FIG. 7 is an enlarged top plan view of a portion of the housing of thefirst embodiment illustrating its display.

FIG. 8 is an enlarged top plan view of another portion of the housing ofthe first embodiment illustrating its keypad.

FIG. 9 is a graphical vertical sectional view illustrating the techniqueof locating a buried sonde with the first embodiment.

FIG. 10 is a graphical vertical sectional view illustrating thetechnique of locating a buried pipe with the first embodiment.

FIG. 11 illustrates a SEARCH view that can be indicated on the displayof the first embodiment.

FIG. 12 illustrates a sonde mode MAP view that can be indicated on thedisplay of the first embodiment.

FIG. 13 illustrates a trace mode MAP view that can be indicated on thedisplay of the first embodiment.

FIG. 14 illustrates an alternate MAP view that can be indicated on thedisplay of the first embodiment.

FIG. 15 is an enlarged view of the underside of the housing of the firstembodiment.

FIG. 16 is a functional block diagram of the analog board of theelectronic circuitry of a second embodiment of our portable batterypowered sonde and line locator that is designed to simultaneously senseand display the location of a plurality of buried objects at the sametime.

FIG. 17 is a functional block diagram of the digital board of theelectronic circuitry of the second embodiment.

FIG. 18 is an enlarged top plan view of a portion of the housing of thesecond embodiment illustrating its display and keypad and showing anexemplary trace mode MAP view in which the locations of a plurality ofdifferent underground utilities are simultaneously visually indicated.

FIGS. 19-22 are additional exemplary trace mode MAP views that can beindicated on the display of the second embodiment.

FIG. 23 is a special set up screen that can be indicated on the displayof the second embodiment.

FIGS. 24-27 are additional exemplary trace mode MAP views that can beindicated on the display of the second embodiment.

FIG. 28 is a perspective view from the top side of a portabletransmitter that can be used with either the first embodiment or thesecond embodiment of our portable sonde and line locator. The pair coilcords and their respective clips that are normally stowed in the pocketsat opposite ends of the transmitter during transport are not illustratedin this view.

FIG. 29 is a reduced perspective view of the transmitter illustratingthe coupling of one of its clips to a ground spike and the coupling ofthe other clip to a gas pipe extending from a gas meter.

FIG. 30 is a perspective view from the bottom side of the transmitterillustrating the to removable mounting of the ground spike to theunderside thereof.

FIG. 31 is a top plan view of the transmitter without its coil cords orclips stowed in the pockets at its opposite ends.

FIG. 32 is an enlarged vertical sectional view of the transmitter takenalong line 32-32 of FIG. 31 showing the coil cords stowed in thepockets.

FIG. 33 is an enlarged perspective view of one of the alligator clips ofthe transmitter that is used to couple a coil cord to a pipe or otherconductor.

FIG. 34 is an enlarged perspective view of a light pipe used in the clipof FIG. 33.

FIG. 35 is a functional block diagram of the electronic circuitry of thetransmitter of FIG. 28.

FIG. 36 is an enlarged view of the display screen and keypad of thetransmitter of FIG. 28.

FIGS. 37-40 are schematic diagrams of several alternate embodiments ofthe LED circuit in the one of the alligator clips of the transmitter.

DETAILED DESCRIPTION OF EMBODIMENTS

Referring to FIG. 2, a first embodiment of the present invention isillustrated in the form of a battery powered, omnidirectional, manuallyportable system 30 that is capable of locating a buried object bysensing an electromagnetic signal emitted by the buried object. Thesystem 30 includes a housing 32 and an elongate member 34 (FIG. 3) thatsupports spaced apart lower and upper sensor balls 36 and 38,respectively, and connects them to the housing 32. The housing 32 (FIG.2) is made of openable rigid plastic shells having a large centralaperture 40 spanned by a handle portion 42.

Circuit means illustrated in FIG. 6 are mounted partly in the housing 32and partly in the sensor balls 36 and 38 for sensing an electromagneticsignal in a frequency range of approximately 50 Hz to 500 kHz emittedfrom a buried object and determining a location and depth of the buriedobject by measuring signal strength and field angles in threedimensions. This is accomplished utilizing a first lower antenna array44 (FIG. 4) and a second upper antenna array 46 (FIG. 5) mounted insidethe lower and upper sensor balls 36 and 38, respectively. The circuitmeans includes a display 48 (FIGS. 2, 6 and 7) for providing a visualindication of the determined location and depth of the buried object.The display 48 is preferably a color or black and white LCD. The circuitmeans of FIG. 6 also includes means for providing an audible indicationwith increasing pitch to indicate to the operator that he or she isgetting nearer to the buried object, including a speaker (notillustrated) mounted behind a grill 50 (FIG. 2) formed in the housing32.

Each of the two antenna arrays, such as the lower antenna array 44 (FIG.4), includes three substantially mutually orthogonal antennas 52, 54 and56. Each antenna is formed by a wire coil such as 52 a wrapped around acircular plastic mandrel 52 b. Each wire coil may be segmented to raisethe self-resonate frequency of the coil and thereby improve the range ofuseful frequencies of electromagnetic signal that can be sensed. Thewire coils and mandrels of each array are progressively smaller so thatthey can be assembled in a nested concentric arrangement. The antennasin each array share a common center point. The elongate member 34 formsan antenna mast and is preferably made from Aluminum or GRP (fiberglass)or other non-ferrous hollow tube. As seen in FIGS. 4 and 5, the elongatemember 34 extends through the nested circular antennas of the arrays 44and 46. The various parts are aligned so that a central axis of theelongate member 34 extends through the pair of common center points ofthe antenna arrays 44 and 46.

The circular antennas of each of the arrays 44 and 46 are nested andpositioned such that an angle subtended between the axis of the elongatemember 34 and each of the circular antennas is substantially identical.In the first embodiment this angle is approximately thirty-five degrees.The mandrels, such as 52 b, of each of the innermost circular antennashave inner curved surfaces that engage the exterior round surface of theelongate member 34. The innermost mandrels may be keyed or otherwisesecured in predetermined vertically spaced positions along the Aluminumtube that forms the elongate member 34. The outer two mandrels of theantenna arrays 44 and 46 interlock with each other and with theinnermost mandrels.

The lower and upper sensor balls 36 and 38 (FIG. 3) each includegenerally spherical elastomeric boots 58 and 60 (FIGS. 4 and 5) whichsurround and enclose the antenna arrays 44 and 46 in a watertightmanner. The lowermost portion of the lower boot 58 (FIG. 4) extendsaround the lower end of the elongate member 34. The uppermost portion ofthe lower boot 58 has a lip which is seated in the peripheral groove ofa grommet 62 that surrounds the elongate member 34. Another grommet 64surrounds the lower end of the elongate member 34. Additional shell-likesupport members 66 and 68 also surround the lower antenna array 44 andhave peripheral lips that fit within the peripheral grooves of thegrommets 62 and 64. A V-shaped pre-amplifier circuit board 70 issupported at an angle relative to the axis of the elongate member 34within the lower antenna array 44 and carries pre-amplifying circuitrythat is connected to the coils of its three mutually orthogonal antennasvia suitable wires and connectors. A connector 72 on the circuit board70 receives a plug (not illustrated) for connecting the pre-amplifyingcircuitry to wires (not illustrated) that extend through a hole (notillustrated) in side of the hollow elongate member 34 and through thehollow central core of the elongate member 34. These wires are connectedto additional circuit boards hereafter described that are mounted withinthe housing 32 and carry the remainder of the circuit means illustratedin FIG. 6. The upper sensor ball 38 illustrated in FIG. 5 has anidentical construction except that both the lowermost and the uppermostportions of the upper boot 60 each have lips which are seated in theperipheral grooves of additional grommets 74 and 76 that surrounds theelongate member 34.

FIG. 6 is a functional block diagram of the electronic circuitry of thefirst embodiment. Most of this circuitry resides on several main circuitboards hereafter described that are mounted within the housing 32,except for the pre-amplifying circuitry that is mounted on separatecircuit boards, such as 70 (FIG. 4), mounted within the sensor balls 36and 38. The pre-amplifier circuit board 70 inside the lower sensor ball36 and the pre-amplifier circuit board 78 mounted inside the uppersensor ball 38 are connected to an analog circuit board 80 (FIG. 6) viamulti-connector twisted pairs, such as CAT-5 network cables. RJ styleconnectors are preferably utilized for quick connection anddisconnection. The analog board 80 contains mixer circuits 82, filteringcircuits 84, gain attenuator circuits 86 and switching circuits 88.

A main digital circuit board 90 sends a single local oscillator (LO)output signal to the analog board 80 and receives amplified and filteredsignals from the antenna coils of the lower and upper antenna arrays 44and 46. The digital circuit 90 board includes a digital signalprocessing (DSP) module 92 and an A/D module 94. The DSP module 92includes digital signal processing circuits, RAM and input/outputcontrol circuits that allow the DSP module 92 to process informationfrom the A/D module 94, configure system settings and enable visible andaudible indications of location and related data to be indicated to theoperator. A flash memory and programmable logic device (PLD) portion 96of the digital board 90 provide system programming, input/out andcontrol logic and LCD driver functions.

The display 48 (FIGS. 2, 6 and 7) is a graphical LCD with a backlight,and its contrast and backlight levels are set by software control. Anaudio generation module 98 (FIG. 6) provides tone signals to a speakerand headphone jack and communications port assembly 100 through a powerboard 102. Besides allowing the connection of a pair of headphones, theassembly 100 permits serial communications, data down load andcalibration functions to be performed. A digital volume control is alsoset by software control. A numerically controlled local oscillator (LO)module 104 on the digital board 90 permits digital frequency controlwhich is set by software control.

A membrane-type keypad 106 (FIGS. 2, 6 and 8) with a light sensor isconnected to a keypad processor 108 (FIG. 6) on the power board 102. Thekeypad processor 108 performs power enable and keypad scanningfunctions. The light sensor in the keypad 106 interfaces with abacklight control circuit 110 for automatically adjusting the level ofthe backlight in the display 48 to compensate for fluctuations in theambient light level. A communications module 112 and sensor A/D module114 on the power board 102 facilitate data communications with apersonal or other computer and interfacing of sensor information to thedigital board 90.

A power supply 116 on the power board 102 receives power from fouralkaline C batteries 118 and converts it to provide all of the requiredvoltages in the system circuitry. For batteries other than alkalinebatteries, the operator uses the keypad 106 and display 48 to set thetype of batteries using a SET UP menu under BATTERY TYPE. This allowsthe system to correctly monitor battery status and advise when power isLOW and the batteries 118 need to be recharged or replaced. The powersupply 116 also provides linear power to the keypad processor 108 forpower management when the system is turned OFF. The system 30 can beconfigured to turn OFF if no commands have been activated or no motiondetected (via optional accelerometer) after a predetermined period oftime has elapsed. It can also provide a visual and/or audible warning inadvance of this automatic shut down and allow the user to interrupt thepower down sequence. The automatic power down feature saves batterypower.

A power processor circuit 120 (FIG. 6) provides power termination,keypad status, system control and sensor feedback (battery voltage,temperature, illumination level, optional accelerometer for motion/leveldetection, backlight control, etc.). Finally, with regard to FIG. 6, anaudio amplifier and headphone switching module 122 supports the speakerand headphone jack and communications port assembly 100.

The first embodiment 30 of the sonde and line locator system of thepresent invention utilizes a graphic user interface (GUI) in the form ofwords, numerical data, menus, symbols and icons to indicate data andlocation information on the display 48 (FIG. 7). This GUI is augmentedby audible tones generated in the internal speaker or headphones thatare driven by the module 122 (FIG. 6) through the audio jack portion ofthe assembly 100. The GUI allows an operator to readily configure thesystem 30 and to easily locate buried objects. The system 30 can beconfigured so that most of the user menus time out if a selection is notmade by the operator within a predetermined amount of time. The system30 can produce two types of sounds, namely, signal sounds and eventsounds. A signal sound is related to increasing or decreasing signalstrength. It is a repeating scale that “winds” up when signal sounds areassociated with some specific occurrence.

Event sounds include:

Equator: Slot Machine

Pole: Clang

Line: Slot machine

Depth Avg. & Hold: Ding—Success

Depth Avg. & Hold: Buzz—Failure [0072] Key Press: Click

Low Battery: Buzz Power Down: Chime Sequence

Startup: Greeting (spoken)

A repeating scale audio tone is used to expand the sensitivity of thesystem 30 to small changes in sensed and visually indicatedelectromagnetic signal amplitude. The audio tone can cycle from low tohigh or high to low in conjunction with numerical values indicated onthe display 48. Hysteresis is built into the tonal switch portion of theaudio amplifier and switching module 122 (FIG. 6) so that the rising andfalling switch points are offset to prevent confusing up and downswitching at the same level of signal strength. If the sound is turnedOFF, all sounds except STARTUP and POWER DOWN are also turned off.

Referring to FIG. 7, the display 48 indicates the sonde frequency 124,sonde level 126, active trace frequency 128, active trace level 130,passive (AC) trace frequency 132, passive (AC) trace level 134, audiolevel 136, battery level 138 and distance (depth) 140. The display 48also indicates the distance units 142, overhead indicator 144, 3D fieldindicator 146, signal strength 148, 2D field indicator 150, horizontalfield angle 152, gain level 154 and current strength 156. A few secondsafter powering up, the system 30 will allow the operator to select anoperating mode from a sonde mode at 512 Hz, an active line trace mode at51 kHz, or a passive AC line trace mode at 60 Hz. The default sondemode, active line trace mode, and passive AC line trace mode frequenciescan be set by software control elsewhere. Any of the three modes can beselected by moving the highlight cursor and pressing the select key 158(FIG. 8) in the center of the keypad 106. The highlight cursor isillustrated in FIG. 7 as a small horizontal rectangle inside the octagonin the display 48. Alternatively, the operator can wait four seconds andthe system 30 will automatically enter the highlighted mode.

Referring again to FIG. 8, the keypad 106 has a number of other keysthat can be manually depressed by the operator to select options andexecute commands. These include a menu key 160 that opens and closes themain menu, a power ON/OFF key 162, an UP key 164 and a DOWN key 166. TheUP key 164 enables the user to scroll up through menu choices, initiatesignal capture, and set the signal and current level to 1000 (“1000 set”explained hereafter) with a long press. The DOWN key 166 enables theuser to set the zero level reference of the system 30, scroll downthrough menu choices, and execute depth average and hold. The DOWN key166 also zeroes the signal strength when held depressed forapproximately three seconds. The select key 158 switches the systembetween SEARCH and MAP views and also selects the choice highlighted onthe display 48 when the system has a menu open. A mode select key 168opens and closes the operating mode menu. A sound key 170 opens andcloses the sound level menu. The operator can cycle the power ON and OFFby depressing key 162 in order to reset 1000 and “set and zero set” todefault levels.

The first embodiment 30 of the sonde and line locator system of thepresent invention uses the multi-directional antenna arrays 44 and 46(FIGS. 4 and 5) along with circuit means (FIG. 6) that includes advancedsoftware programming to make pinpointing sondes and tracing buried linesfast, accurate and easy. The GUI implemented via the display 48 (FIGS. 2and 7) allows the operator to “see” the fields and to quickly resolvecomplex locating problems. The first embodiment 30 measures and displayselectromagnetic fields emitted by long conductors such as energizedwires, video inspection camera push cables, conduit or pipes when in itstracing mode. The passive AC tracing mode is a specialized case of thetracing mode where the line is already energized with 50 or 60 Hzelectrical power. Active transmitters such as sondes are located in thesonde mode. Unlike conventional paddle or stick locators, which can onlymeasure signal strength in the direction of the individual antenna(s),the first embodiment 30 measures both signal strength and field anglesin three dimensions (3D). This enhanced capability makes it possible forthe first embodiment 30 to indicate a mapping display on the LCD 48.

FIG. 9 is a graphical vertical sectional view illustrating the techniqueof locating a buried sonde 10 with the first embodiment 30. The sonde 10is “seen” only as a single peak 130 and there are no confusing nulls orfalse peaks. Compare this technique to the prior art approachillustrated in FIG. 1.

FIG. 10 is a graphical vertical sectional view illustrating thetechnique of locating a metal pipe 132 buried in a concrete slab 134with the first embodiment 30. The pipe 132 has a signal applied theretowhich generates a long cylindrical electromagnetic field illustrated byconcentric circles 136. The pipe 132 is “seen” by the first embodiment30 as a single peak 138 directly above the pipe 132, without any nullsor false peaks.

The first embodiment 30 offers the following advantages overconventional sonde and line locators. First, the sensed electromagneticsignal always gets stronger as the operator carrying the firstembodiment 30 gets closer to the buried object. Second, nulls and false(“ghost”) peaks are eliminated. With conventional locators, it ispossible to have signal strength go up as the operator moves away fromthe buried object. A conventional locator “sees” a larger peak, then anull, and then a smaller peak. This can confuse the operator especiallyif he or she interprets a smaller peak (known as a ghost or false peak)as the buried object. Third, the orientation of the first embodiment 30relative to the buried object does not have any effect on sensed signalstrength. The operator can approach from any angle with the firstembodiment 30 held in any orientation and he or she need not know thelie of the pipe or wire. Conventional sonde and line locators must beorientated in a specific manner to locate a sonde or trace a line oncethe initial signal has been picked up. Fourth, the first embodiment 30facilitates the solution of difficult location tasks by indicatinggraphical map views and angle indicators on the display 48 to helpinterpret electromagnetic signal characteristics.

Each of the three modes of operation of the first embodiment (sondemode, line trace mode and AC line trace mode) has two views that can beindicated on the display 48, namely, a SEARCH view and a MAP view. TheSEARCH view emphasizes locating based on signal strength and it is thedefault view for the sonde mode. The MAP view emphasizes locating basedon field angles and is the default view for the line trace and AC linetrace modes.

Referring to FIG. 11, in the SEARCH view a numeric (digital) signalstrength is indicated at 172 on the display 48. This number gets largeras the system 30 gets closer to the buried object and the sensedelectromagnetic signal gets stronger. This number gets smaller as thesystem 30 gets further away from the buried object and the sensedelectromagnetic signal gets weaker. An octagonal “track” pattern 174 hasa rectangular signal strength indicator 176 with an internal chevronsymbol that continuously moves in a non-linear manner around the pattern174 to indicate the change in sensed electromagnetic signal strength.Clockwise movement of the indicator 176 represents increased signalstrength whereas counter-clockwise movement of the indicator 176represents decreased signal strength. Thus, the moving signal strengthindicator 176 provides a convenient analog representation of thevariation in sensed signal strength. Each revolution of the indicator176 around the octagonal pattern 174 is matched by a correspondingaudible tone or sound that indicates larger or smaller sensed signalstrength. A naked chevron maximum signal marker 178 marks the point ofmaximum signal strength and appears when the sensed signal begins todecrease. In the SEARCH VIEW, each revolution of the signal strengthindicator 176 is accompanied by a tonal amp, which can repeat for eachrevolution. This provides an audible indication that represents both thedirection and amount of signal sensed and mirrors the same informationshown on the display 48 by the indicator 176.

The octagonal pattern 174 (FIG. 11) and the indicator 176 that travelsaround the same in a generally circular fashion provide a visual analogindication to an operator that represents the variation in sensed signalstrength. The pattern 174 need not be octagonal in shape, but could besquare, circular, oval, etc. The pattern 174 yields an importantadvantage in that it provides an interior space inside the “track” wherethe digital signal strength 172 and a mini-map 180 can be displayed. Themini-map 180 represents a condensed version of the MAP view hereafterdescribed. The MAP view shows visual cues that guide the operator towardthe source of the signal in the different modes as explained.

Referring to FIG. 12, when the sonde mode MAP view is shown on thedisplay 48 of the system 30 a sonde axis is indicated at 182. This axisrepresents the approximate direction of the pipe when the system 30 ispositioned above the pipe and between the poles. A zoom ring 184magnifies the area when the first embodiment 30 is close to a pole formore accurate pole location. The zoom ring 184 represents a zoomed outsearch area adjacent to the pole. The equator is indicated by a dottedline 186 and a pole symbol/icon is indicated at 188. The equator is thepoint where the field lines are flat or horizontal. As in the earthmodel, the equator is the line at zero degrees latitude. At the pointwhen the field lines are straight up and down, or vertical, this iscalled a pole. Poles are distinct points, not lines like the equator.The GUI of the system 30 displays the equator 186 (FIG. 12) where thefield angle above the sonde is zero degrees. Event sounds can also begenerated in conjunction with this display. These include specificsounds when the system 30 is positioned over the pole, or over theequator, or when other states occur, like low battery.

Referring to FIG. 13, when the trace mode MAP view is shown on thedisplay 48 of the system 30 a solid graphic line 190 represents aposition of an energized line as measured by the lower antenna array 44.The dotted line 192 presents the position of an energized line asmeasured by the upper antenna array 46. The solid graphic line 190 thatindicates the location of the system 30 and moves side-to-side on thedisplay with respect to a buried object emitting an electromagneticfield that is approximately cylindrical using the measured angle of thefield with respect to the system 30. If the measured field angle is zerodegrees (orthogonal to the longitudinal axis of the antenna mast 34) theGUI of the system 30 will display the line 190 centered on the display48. The solid graphic line 190 is also displayed offset from the centerof the display 48 in an amount proportional to the measured tilt of thefield. The direction of the offset is set by the direction of tilt ofthe measured field. The field angle does not have to be explicitlycalculated in order to accomplish the foregoing. However, somethingequivalent thereto must be calculated. This could be done with ratios,but they would be reducible to their field angle equivalents. Thepresence of any distortion or interference in the field of interest willcause the solid graphic line 190 and the dotted line 192 to move out ofalignment. A sound event, such as increasing pitch, can also begenerated to indicate nearness and/or to indicate which side of thesolid graphic line 190 the system 30 is located on. Such a sound eventcould be a synthesized voice saying LEFT or RIGHT.

The GUI of the system 30 can also display lines as described above indifferent colors or labeled in a different way for each of the twoantenna arrays 44 and 46. The GUI of the system 30 can also displaypoles 188 and the equator 186 when locating a buried object with dipolefield, e.g. a sonde. The graphical display can be configured as a radarscope type display screen where a “pole” is displayed in the center ofthe screen if the field is vertical (ninety degrees) and thenproportionally offset from the center of the display screen dependingupon the direction and the degree of tilt of the field, either withrespect to the system 30 itself or with respect to a verticallycorrected orientation if a gravity sensor is incorporated into thesystem.

Referring to FIG. 14, an alternate sonde mode MAP view can be shown onthe display 48 of the system 30 in which the orientation of the pipe isrepresented by a pair of parallel lines 196 which are broken in theirintermediate region, which corresponds to the equator, to indicatepositional uncertainty when the operator is standing on the equator.Clearly, a pipe or other conduit must exist in order for a sonde to beinserted into the same so the parallel lines 196 indicate the sondeaxis. The lines 196 move or rotate as the operator walks around abovethe sonde. The dotted line 198 represents the equator and the icon 200indicates that the system 30 is in its sonde mode. The sonde icon 200alternates from one end of the equator to the other. The dashedcross-hair 202 represents the center point of the display 48. The smalltriangular symbols or brackets 204 on either side of the digital signalstrength number 206 are displayed whenever the current signal strengthshown is equal to the largest value stored in memory for the currentlocating session (since POWER UP). This allows the operator to movealong the equator and then stop as soon as the peak (strongest sensedsignal) is passed. As soon as the signal strength begins to decrease,the brackets 204 and the sonde sound event turn OFF. When the operatorreverses direction and returns to a point of equal or greater signalstrength the brackets 204 reappear and the sound event returns.

The system 30 measures depth by comparing the strength of the signaldetected by the lower antenna array 44 to that detected by the upperantenna array 46. The system 30 need not have upper and lower arrays toaccomplish depth measurement, and indeed depth could be measured usingonly a single one of the arrays 44 or 46 that includes three mutuallyorthogonal antennas with a fourth antenna spaced above or below thearray. In order to accurately measure the depth of the buried object theelongate member 34 which functions as the antenna mast should be pointedat the source of the electromagnetic signal. The actual depth ismeasured when the lower sensor ball 36 is touching the ground directlyabove the buried object. Alternatively, the distance to the buriedobject can be measured when the lower sensor ball 36 is not touching theground. It will be understood by those skilled in the art that thesystem 30 need not have depth measuring capability, in which case asingle antenna array such as 44 would suffice, but as a practicalmatter, a commercially viable sonde and line locator needs to include adepth measuring capability. It may be possible to mount the upperantenna or antenna array 46 inside the housing 32 instead of on theelongate member, but this may subject the antenna or array to excessivenoise from the microelectronic circuitry on the circuit boards 80, 90and 102 (FIG. 6).

There are two ways that the system 30 can measure and indicate the depthof the buried object. It can indicate real time depth continuously inthe bottom left corner of the display 48 at 140 (FIG. 7). Alternatively,by pressing and releasing the DOWN key 166 (FIG. 8) the display 48 willindicate in large numbers in the center thereof a “count down” from fourseconds, second by second. During this count down the system 30 willmeasure the depth and average the measurements, and filially display theaverage depth in the lower left hand corner of the display 48 at 140.

The system 30 displays the overhead indicator 144 (FIG. 7) on the LCD 48if the upper antenna array 46 receives more signal than the lowerantenna array 44. Typically this tells the operator that an overheadsource of electromagnetic signal is present, such as an overhead ACpower line. Negative depths can be indicated by illuminating theoverhead indicator rather than a single negative number.

Pressing the UP key 164 (FIG. 8) when the system 30 is in the SEARCH orMAP view will save the current signal strength to temporary memory andhold the same until the system 30 is turned OFF. This value is displayedat location 148 (FIG. 7) on the display 48 when in the SEARCH view. Ifthe operator saves the current signal strength while in the MAP view heor she will need to switch to the SEARCH view in order to see the same.This feature can be used to compare the signal strength of the two poleswhen locating a sonde. A level sonde under level ground will have thesame signal strength at each pole. If the sonde is inclined, the upwardtilting end will be read as a higher signal strength. If the sonde isnear a transition in a pipe type, e.g. going from ABS plastic to castiron, the cast iron end of the pipe may be read as a lower signalstrength.

The system 30 indicates the relative current strength at 156 (FIG. 7) onthe display 48. This helps the operator see any drop in signal strengththat may indicate a junction in the line or if the line splits. Thecurrent signal strength also verifies that the correct line is beingtraced as signal strength may bleed over to shallower lines. Theseshallower lines may be read as having similar signal strength but thecurrent strength may be lower.

At the beginning of the effort to locate a buried object with the system30 it is helpful to have the system 30 read “0.0” for the startingpoint. Due to other interference signals this may not be the case. Thetemporary zero set command is a valuable tool that can be used forsingle locate environments where there is some interference present.This helps the system 30 sense only that signal that is emitted by thesonde or line since it zeroes out the other signals before the sonde orline transmitter is turned ON. When the sonde or line transmitter signalis turned ON then the apparent sensitivity will be set to read only thatsignal.

The system 30 can also be set to read 1000 when directly over the buriedobject. This gives the operator a maximum signal strength value that cansimplify tracing. The 1000 set feature references the current signallevel to the displayed value of 1000 and re-maps the sensitivity of thecircuit to represent the range of signals between the reference levelstored at the zero set, and the reference at the 1000 set to thenumerically displayed range of 0 to 1000. During a line trace the 1000set feature makes it easier for the operator to stay on the line andalso see changes in signal level. Signal strength varies as the linedepth changes. If the line splits the signal strength drops since aportion of the signal then travels along one leg of the split and theremaining portion travels along the other leg. For example if thedisplayed signal strength has dropped to 500 the measured signal hasdropped by fifty percent.

The system 30 permits the signal strength value for the frequency ofinterest in different modes to be temporarily set to zero or permanentlyset to zero. The permanent zero set feature allows the operator toadjust the minimum level of electromagnetic signal that will be shown onthe display 48. This allows the system 30 to effectively disregardsignals smaller than the consistent ambient noise level. It is useful tohave the system read “0.0” when no signal is present as a starting outpoint or base line. Some operators will prefer maximum sensitivity whileothers prefer to only show signal when it is strong and well above anyinterfering noise signals. Environmental noise may be very high inindustrial areas and very low in rural areas. The permanent zero setfeature allows the operator to effectively tune the system 30 to work inoptimal fashion in a given environment and to meet the operator'spersonal preferences. Typically the user would take the system 30 to a“quiet spot” on the site, with no signal present, and then adjust thesignal strength to “0.0”. Then any signals larger than this will be readand indicated as some larger value.

The system 30 also indicates an icon in the form of a globe 194 (FIGS.7, 11, 12 and 13) in which the measured field angle is indicated asbeing located on the pole if it is at ninety degrees and indicated asbeing on the equator if it is at zero degrees.

A plurality of brightly colored plastic marker chips 210 (FIG. 15) areremoveably mounted on a post 212 that extends from the elongate member34, directly beneath the housing 32. These marker chips 210 can beremoved and placed on the ground to facilitate the process of locating asonde or tracing a line with the system 30. The marker chips 210 havestarred apertures with deflectable fingers that allow them to snap fitover a flared outer end of the post 212. The inner end of the post 212can be secured to the elongate member 34 in any suitable fashion, suchas with a molded plastic U-shaped clamp (not shown). The clamp snaps onthe elongate member 34 and can slide and rotate. Preferably, there aretwo orange triangular shaped marker chips 210 that can be placed on theground to mark the poles, and a single yellow octagonal marker chip 210that can be placed on the ground to mark the location of the sonde. Aknob 214 can be rotated counter clockwise to remove a door 216 thatcovers the compartment for the batteries 118. A synthetic rubber bumper218 surrounds the housing 32. A helpful icon reference label 220 isaffixed to the underside of the housing 32. A serial number label 222also affixed to the underside of the housing 32 bears a unique numberand bar code that identifies the specific system 30 from all similarsystems that have been manufactured.

From the foregoing detailed description it will also be appreciated thatthe present invention also provides a method of locating a buried objectby sensing an electromagnetic signal emitted by the buried object.Broadly, the method includes an initial step of traversing a topsidearea beneath which an object emitting the electromagnetic signal isburied with at least one antenna array 44 including three substantiallymutually orthogonal antennas. The method further includes the step ofsensing the electromagnetic signal emitted by the buried object with thearray 44. The method also includes the step of determining a location ofthe buried object based on the sensed electromagnetic signal withouthaving to align the antenna array 44 relative to the buried object whileeliminating nulls 24 and 26 (FIG. 1) and false peaks 18 and 20. In orderto measure depth, while avoiding a null detection, the topside area issimultaneously traversed with the second antenna array 46 that includesat least a pair of antennas.

In order for the system 30 to correctly sense the total field vector,the response of each coil within each of the arrays 44 and 46 needs tobe calibrated with respect to the response of the other two coils withinthe same array. The geometry of the antenna arrays 44 and 46 and themanner in which they are mounted to the elongate member 34 greatlyfacilitates the calibration of the system 30. Conventional sonde andline locators typically have at least one antenna in their array thathas an axis that is substantially in alignment with part of thesupporting structure. If any one of the antennas in the array has itsaxis orthogonal to the axis of the calibrating field, then it is notpossible to calibrate that antenna as its response will be nominallyzero. The system 30 has a preferable geometry where each antenna hassubstantially the same offset angle relative to the axis of the elongatemember or antenna mast 34. This makes it possible to calibrate each ofthe three antennas in each array relative to the other two antennas inthe same array. This can be done by placing the system 30 within atubular solenoid field. The two antenna arrays 44 and 46 need to be veryaccurately aligned and centered within the solenoid calibration field.The solenoid field must be substantially cylindrical so that a uniform,rotationally symmetric calibration field is generated. Making theantenna arrays 44 and 46 spherical and enclosing them in the sensorballs 36 and 38 allows a fixture to be constructed for readily centeringthe calibration field relative to the elongate member or antenna mast34. Furthermore, making the antenna arrays 44 and 46 relatively smalland round, and precisely centering these antenna arrays on the elongatemember 34 minimizes the mass of the shielding required on thecalibration chamber.

FIG. 16 is a functional block diagram of the analog board 80′ of theelectronic circuitry of a second embodiment of our portable batterypowered sonde and line locator that is designed to simultaneously senseand display the location of a plurality of buried objects at the sametime. It is similar to the analog board 80 of the first embodiment 30except that the former includes more mixers 224 for processing thevarious signals in different frequency bands that are received by all ofthe antennas. FIG. 17 is a functional block diagram of the digital board90′ of the electronic circuitry of the second embodiment. It is similarto the digital board 90 of the first embodiment 30 except that theformer includes a plurality of numerically controlled local oscillator(LO) modules 226 that send a plurality of output signals to the analogboard 80′. The modified digital board 90′ receives amplified andfiltered signals from the antenna coils of the lower and upper antennaarrays 44 and 46 in a fashion similar to that of the digital board 90,except that the former is simultaneously processing signals generated indifferent frequency bands.

The second embodiment allows the user to seek and locate electromagneticsignals emitted by different buried objects at different frequencies.Preferably the second embodiment allows the user to select betweendifferent frequency bands separated by orders of magnitude, e.g.frequency bands centered on 100 Hz, 1 kHz, 10 kHz and 100 kHz, andwithin different channels within the bands. Preferably, the channelswithin each band are separated by some uniform amount, e.g. 10 Hz or 100Hz.

The mechanical and electro-mechanical aspects of the second embodimentare similar to those of the first embodiment illustrated in FIG. 2except as otherwise indicated hereafter. Throughout this descriptionlike reference numerals refer to like parts. The software of the secondembodiment is designed to enable a plurality of different buried objectsto be simultaneously detected and their locations and depthssimultaneously indicated visually and/or audibly.

FIG. 18 is an enlarged top plan view of a portion of the housing 32 ofthe second embodiment illustrating its display 48 and keypad 106 andshowing an exemplary trace mode MAP view in which the locations of aplurality of different underground utilities are simultaneously visuallyindicated. A phone utility icon 228 is indicated on the display 48without the line orientation feature selected. An electric utility icon230 is indicated on the display 48 with the line orientation featureselected and indicated by a solid bold diagonal line 232. A 60 Hz icon234 is indicated on the display 48 without the line orientation featureselected. A gas utility icon 236 is indicated on the display 48 withoutthe line orientation feature selected.

Continuing with FIG. 18, if a sonde is being used, the sonde frequencyand level are indicated at a location 238 in the upper left corner ofthe display 48. No values for the sonde frequency and level areillustrated in FIG. 18. High, medium and low frequencies are indicatedby unique corresponding wave form patterns 240. The icon of thecurrently selected utility, in this case the electric utility, is shownat 230′ in the upper left corner of the display 48. An AC trace levelcan be indicated at location 242. In FIG. 18, no AC trace level isillustrated. The audio level currently selected on the second embodimentis illustrated by the bar graph 244 on the display 48. The level of thecurrently selected battery type used in the second embodiment isillustrated by the bar graph 246 on the display 48. The depth ordistance of the currently selected utility is indicated on the displayat 248 which in the example of FIG. 18 is ten inches. A 3D fieldindicator is indicated by the octagon 250 and a signal strength for theselected utility is indicated at 252, which in the example of FIG. 18 is1182. A 2D horizontal field indicator is indicated at 254. Thehorizontal angle is digitally indicated on the display 48 at 256 whichin the example of FIG. 18 is two degrees. A small graphic tab or notch258 moves clockwise along a large octagonal race track 260 in aclockwise direction to indicate increasing field strength and in acounter-clockwise direction to indicate decreasing field strength. Anauto-gain step is digitally indicated at a location 262 which in theexample of FIG. 18 is a 3. Finally, a source current level is indicatedon the display 48 of the second embodiment at a location 264 which inthe example of FIG. 18 is 1999. All highlighted information indicatedaround the periphery of the display 48 of the second embodiment thatpertains to a specific selected utility will change when the selectedutility is changed. Different utilities can be selected by pressing theselect key 158 in the center of the keypad 106.

FIGS. 19-27 are additional exemplary trace mode MAP views that can beindicated on the display of the second embodiment. FIGS. 19-22correspond to, and demonstrate how the screen on the display 48 changesas the display “focus” is switched from one utility to the next byactuation of, for example, the select key 158. In the case of FIGS.19-22 there are a total of four utilities active, one of which is apassive 60 Hz source. The selected utility in each case is shown with abold line through its icon while the others only show short “tails.” Thebold line 232 indicates the orientation of the selected utility. Theshort tails on the non-selected utilities show the approximateorientation of the electromagnetic fields associated with eachcorresponding sensed frequency. Grey scale or other methods could beused to indicate the unselected utilities. All of the field or signalspecific data changes each time a different utility is selected. Theindicated field strength, field angles, current and depth are specificto each selected utility. The signal from the upper antenna ball 38(dashed line 266) also changes in the screens illustrated in FIGS.20-22. The corresponding one of the icons 228, 230, 234 and 236 isindicated in the upper left corner of the display 48 changes to indicatethe currently selected utility.

Besides visual indications of the different locations of the differentutilities, the second embodiment can give audible indications such astones, synthesized human voices, or musical voices. For example, thesecond embodiment could tell the user “sewer two feet left” then “sewerone foot left” then “above sewer” as the user moves the line locator tothe left. The second embodiment could also say “turn right” or “turnleft” if the angle between the traced line and the locator is greaterthan some pre-programmed value. The audible turn indicators could alsogive the magnitude, e.g. “turn, right, two.” Musical voices couldinclude a tuba for sewer, a claxon for electric, etc.

FIG. 23 illustrates a special set up screen that can be indicated on thedisplay 48 of the second embodiment. It allows the user to adjust theamount of signal discrimination. If the electromagnetic signal is lessthan some specified value the signal strength for that utility isindicated as zero. This allows the user to have the display 48 onlyindicate strong, valid signals. This helps the user in many situationsin sorting out “noise” from the target signals of interest. This featureof the second embodiment is similar to the “zero set” feature of thefirst embodiment except that the former allows the “strength” of thezero set to be varied as needed. Preferably, the second embodimentallows the user to individually set a zero threshold (and also 1000magnitude set) for each utility separately and individually, and to savethis information. It also preferably allows the user to reset each zeroat any time during the location process to manage or minimize cross-talkor coupling between different lines. The zero threshold can be used as acriteria or trigger to display or not display any of a plurality ofutilities. For example, if the signal strength of the target utility isless than a reference level, and the locus of the locator is set toanother utility subchannel, then the second embodiment will not display(or alter the display) of that utility.

FIG. 24 illustrates the manner in which the display 48 of the secondembodiment indicates the location of a marker ball illustrated by theunique icon 268. Preferably the configuration of the icon 268 can bevaried to indicate different types of buried utility makers, alsosometimes referred to as marker balls, locator pegs and marker discs.

FIG. 25 illustrates an alternate way of indicating different types ofutilities on the display 48 of the second embodiment. In this example,the user is tracing multiple gas lines G1, G2, etc. However, the displaycould also indicate W, G, E, etc. for water, gas, electric, and soforth. Simple numerals like 1, 2, 3, etc. could also be used.

FIG. 26 illustrates the manner in which the second embodiment can changethe selected utility trace line from bold to dashed if the measureddepth is negative. If the measured depth is negative, the signal sourceis either above the locator (user) or the signal is highly distorted orperhaps mostly attributable to noise. In any event, the secondembodiment preferably has the capability of indicating a measure ofuncertainty in how information is displayed to the user.

FIG. 27 illustrates the manner in which the second embodiment canindicate information encoded on trace signals placed on utilities. Inthis example an 800 phone number has been detected and indicated on thedisplay 48.

FIG. 28 is a perspective view from the top side of a portabletransmitter 270 that can be used with either the first embodiment or thesecond embodiment of our portable sonde and line locator. It will beunderstood that a user will need several transmitters of this type toenergize each different utility with the appropriate electric signal.The transmitter 270 includes a hollow molded plastic portable housing272 preferably having a pair of outwardly and upwardly openingreceptacles or pockets 274 and 276 at opposite ends thereof. Ahorizontal control panel 278 is mounted on the top side of the housing272 for receiving manually inputted commands. The control panel 278includes a membrane type keypad 280 with a plurality of individualpushbutton keys 280′. The control panel 278 further includes a pluralityof individual colored LEDs 281, many of which are associated with aparticular one of the keys 280. Additional LEDs 280 on the control panel278 are not associated with a particular key 280 but will indicate awarning or status conditions such as the presence of high voltage at theoutput coupling. An LCD display 282 also forms a part of the controlpanel 278. On the control panel 278 of the transmitter 270, the manualselection of different frequencies for activating and tracing variousutility lines follows the colors normally associated with particulartypes of utilities. Electricity is indicated by an illuminated red LED,gas is indicated by an illuminated yellow LED, sewer is indicated by anilluminated green LED, water is indicated by an illuminated blue LED andcommunications is indicated by an illuminated orange LED.

An electronic circuit 284 illustrated in block diagram form in FIG. 35is physically supported on one or more printed circuit boards (notillustrated) mounted inside the housing 272 (FIG. 28). The electroniccircuit 284 receives commands from the control panel 278 and generates apredetermined electrical output signal in response to the commands. Moreparticularly the electronic circuit 284 of the transmitter 270 allowsthe user to select from a plurality of frequency bands each separated byan order of magnitude, and then from a plurality or cluster of signalswithin those bands. By way of example, the frequency bands may becentered on 100 Hz, 1 kHz, 10 kHz and 100 kHz. The channels within eachband are stepped or spaced suitable equal intervals apart, such as 10Hz, to allow them to be readily discriminated, as is well known in theart. Preferably the electronic circuit 284 is also able to generate veryhigh frequency signal, such as 480 kHz, for specialized tracingactivities. The second embodiment of the locator can be programmed toseek this frequency. The transmitter 270 can also generate singlefrequencies not spaced apart by orders of magnitude.

Referring to FIG. 35, the electronic circuit 284 of the transmitter 270includes a central processor circuit 286 including A/D converter 288,EEPROM 290 and a pulse width modulator (PWM) 292 for generating theaudio drive signal for a buzzer type annunciator 294. The centralprocessor circuit 286 drives the LCD display 282 and the backlight drive296 for the display 282. The electronic circuit 284 also includes acontrast adjust circuit 298.

The electronic circuit 284 of the transmitter 270 further includes apower supply 300 having a plurality of replaceable batteries 302, suchas eight C type alkaline cells. The central processor circuit 286receives power from the power supply 300 via a linear regulator circuit306. The central processor circuit 286 controls power to the rest of thesystem by switching a system power circuit 304. The central processorcircuit 286 also controls a boost switching power supply (SPS) 308 toset a variable output voltage (Vboost) which is fed to a power drivecircuit 330. The voltage at the batteries 302 and optionally the outputof the boost SPS 308 are fed to the A/D converter 288 to measure batteryvoltage in order to estimate remaining battery power and boost voltage.A frequency synthesis circuit 310 is connected between the centralprocessor circuit 286 and a drive and feedback circuit 312. Thefrequency synthesis circuit includes a first numerically controlledoscillator (NCO) circuit 314 that generates a base frequency and asecond numerically controlled oscillator (NCO) circuit 316 thatgenerates a so-called “sniff” frequency to facilitate location. By wayof example, the sniff frequency may be a very high frequency, such as480 kHz. The outputs of the first NCO circuit 314 and the second NCOcircuit 316 may be adjusted through variable amplifiers 318 and 320,respectively. The central processor circuit 286 controls the NCOcircuits 314 and 316 via F select lines 322 and 324, respectively. Thecentral processor circuit 286 controls the variable amplifier 318 viabase level line 326 and controls the variable amplifier 320 via tracelevel line 328.

The drive and feedback circuit 312 includes the power drive circuit 330that receives an electric signal with a preselected voltage directlyfrom the boost SPS circuit 308 and the amplified signals from the NCOcircuits 314 and 316 and the variable amplifiers 318 and 320. The outputsignal of the power drive circuit 330 is fed through a current sensecircuit 332 that provides an output sense voltage proportional to thedrive current. This sense voltage is fed to the A/D converter 288 tomeasure the current. The power drive signal is then fed to an outputvoltage sense circuit 334 which provides an output sense voltageproportional to the drive voltage. This sense voltage is fed to the A/Dconverter 288 to measure the output voltage. The current sense andvoltage sense signals are used to determine the power being delivered tothe load. The power drive signal is then fed through an output driveprotection circuit 336 which protects the drive and feedback circuits312 from be damaged by connection to an external power source such as alive high voltage wire. The output drive protection circuit 336 containsa fuse as well as filtering and clamping circuits. The power drivesignal is then fed from the output drive protection circuit 336 into adrive routing circuit 338 that includes manually actuated drive andinductive clamp switches 340 and 342 that allow the final output signalof the electronic circuit 284 of the transmitter 270 to be coupled to aselected utility via coupling means such as an inductive antenna 344, aninductive clamp 346 or a coil cord connector 348.

Referring to FIG. 29, in one configuration of the transmitter 270 a pairof electrical cords 350 and 352 are each stowable in a corresponding oneof the pockets 274 and 276. The electrical cords each have a conductorwith an inner end that is electrically connected to the electroniccircuit 284. Preferably the electrical cords 350 and 352 are of thespringy helical coil type that readily stretch and contract. The cords350 and 352 should be as small and lightweight as possible so that theirlengths can be maximized and they will still fit within their respectivepockets 274 and 276. We have found that the inner conductors of the coilcords 350 and 352 which are covered with plastic insulation can be madeof steel instead of the usual Copper found in such cords. Steel is muchstronger than Copper and therefore the conductors can be made smaller.The higher electrical resistance is acceptable in a transmitterapplication as the resistance of the types of circuits (utilities) towhich the transmitter 270 will typically be connected is high.

Referring still to FIG. 29, alligator style clips 354 and 356 withspring biased opposing electrically conductive jaws are electricallyconnected to the outer ends of the conductors in each of the electricalcords 350 and 352 for coupling the predetermined electrical signalacross a selected utility line which, in FIG. 29, is a gas line 358. Thegas line 358 joins with an above-ground gas meter 360 and a majority ofits length extends underground. The alligator clip 356 is connected tothe conductor of the coil cord 352 which is in turn connected to thepositive electrical output signal of the electronic circuit 284 via thedrive routing circuit 338. The alligator clip 356 is clamped around thegas line 358 to energize the same so that it emits electromagneticradiation at the desired frequency for optimum tracing. The otheralligator clip 354 is connected to the outer end of the conductor of thecoil cord 350 which is in turn connected to the ground side of theelectronic circuit 284. The alligator clip 354 is clamped around theupper portion of a T-shaped steel ground spike 362 that is driven intothe soil to complete the circuit across the gas line 358.

FIG. 29 also illustrates a pivotal handle 364 of the transmitter in itsraised position. The handle 364 is generally U-shaped and the lower endsof its legs are pivotally connected to opposite sides of the housing 272near the control panel 278. The intermediate segment of the handle 364can be grasped by a user to lift and carry the transmitter 270 to thelocation of the above-ground portion of the utility that is to beenergized.

FIG. 30 is a perspective view from the bottom side of the transmitter270 illustrating the removable mounting of the ground spike 362 thereto.A removable bottom wall 366 of the housing 272 has a pair of spacedapart sleeves 368 and 370 formed therein which slidingly receive thepointed round shaft portion 362 a of the ground spike 362. A pair ofshoulders 372 and 374 are also formed on the bottom wall 366 adjacentthe sleeves 368 and 370, respectively. The shaft portion 362 a ridesover the shoulders 372 and 374 to provide a snug fit. Curved pairs ofopposing guide walls 376 and 378 are connected to the bottom wall 366before the first sleeve 368 and after the second sleeve 370 so that theground spike 362 can be inserted from either end of the housing 272 andthe handle portion 362 b thereof will be received in one of theconformably shaped handle receiving slots such as 380 formed at eitherend of the housing 272. The pointed shaft portion 362 a of the groundspike 362 is preferably made of steel while the handle portion 362 b ispreferably molded from plastic and rigidly secured to the blunt end ofthe shaft portion 362 a. The bottom wall 366 of the housing 272 of thetransmitter 270 is formed with a pair of diagonally located key-holeshaped apertures 382 and 384 that allow a bicycle or other locking cableto be passed through one of the pockets 274 and 276 to lock thetransmitter 270 to a gas pipe or other fixture to prevent thetransmitter from being stolen. A gasket or boot 386 made of a suitableelastomer such as synthetic rubber surrounds the base of the housing 272and provides a water tight seal between the removable bottom wall 366and the remainder of the housing 272. The boot 386 deforms to is allowthe handle portion 362 b of the ground spike 362 to move past the sameupon insertion thereof into the sleeves 368 and 370 and helps retain theground spike 362 in its loaded and stored position illustrated in FIG.30.

Referring still to FIG. 30, access to the eight C cell alkalinebatteries 302 is accomplished by unscrewing a knob 388 to permit removalof a battery compartment cover 390. A removable fuse 392 may beunscrewed and replaced. The fuse is part of the output drive protectioncircuit 336. A female headphone type jack 394 is provided for theconnection of an inductive clamp (not illustrated). A power type jack396 permits an auxiliary power source to be connected to the electroniccircuit 284.

FIG. 31 is a top plan view of the transmitter 270 without its coil cords350 and 352 or alligator clips stowed in the pockets 274 and 276 at itsopposite ends. A pair of drain holes 398 and 400 formed in the bottomwall 366 are visible in this figure.

FIG. 32 is an enlarged sectional view of the transmitter taken alongline 32-32 of FIG. 31 showing the coil cords 350 and 352 stowed in thepockets 274 and 276, respectively. Four of the C cell batteries 302 arealso visible in this figure.

FIG. 33 is an enlarged perspective view of one of the alligator clips356 of the transmitter 270 that is used to couple the coil cord 352 tothe gas pipe 358. One of the jaw handles 402 is provided with acylindrical over-molding 404 that houses and protects one or more LEDsand supporting circuitry hereafter described. The illumination fromthese LEDs is made visible by means of light pipe 406. Illumination fromthese LEDs provides visual feedback to the user that the line or cableto which the jaws 408 and 410 have been clamped is receiving the outputsignal of the transmitter 270. FIG. 34 is an enlarged perspective viewof one configuration for the light pipe 406 used in the alligator clip356 illustrated in FIG. 33 that enables three hundred sixty degreeviewing. This configuration can only accept one LED at a time but thelight pipe could be modified to receive and transmit the light from aplurality of LEDs simultaneously.

FIG. 36 is an enlarged view of the control panel 278 of the transmitter270 illustrating details of its display screen 282 and its keypad 280 ofthe transmitter 270. The keypad 280 has a number keys or pushbuttonsthat can be manually depressed by the user to select options and executevarious commands. The keypad 280 includes UP, DOWN and SELECTpushbuttons 412, 414 and 416, respectively. There are six differentpushbuttons with graphics for six different types of utilities, eachhaving an associated LED 281 of the appropriate color which isilluminated when that pushbutton is depressed. The reference numeral280′ and its lead line point to the pushbutton for selection of thecommunications utility. A menu key 418 opens and closes the main menu,selections from which are indicated on the display 282 and may bescrolled through and selected via actuation of pushbuttons 412, 414 and416. A power ON/OFF pushbutton 420 allows the transmitter 270 to beturned ON and OFF. A sound pushbutton 422 opens and closes the soundlevel menu. The control panel 278 also has three frequency modeselection pushbuttons 424, 426 and 428 situated in a vertical row to theright of the UP, DOWN and SELECT pushbuttons 412, 414 and 416. Finallythe control panel has a separate warning LED 430 that is illuminated towarn the user that a hazardous voltage is present. The central processorcircuit 286 has all the intelligence and programming for providing auser friendly graphical user interface (GUI) on the LCD display 282, oneexample of which is illustrated in FIG. 36.

FIGS. 37-40 are schematic diagrams of several alternate embodiments ofthe LED circuit in the alligator clip 356 of the transmitter 270. In thecircuit of FIG. 37 two LEDs 432 and 434 are oppositely oriented andconnected in parallel. The LED 432 is connected in series with theoutput cable 352. While this circuit provides the brightestillumination, special LEDs are required. In the circuit of FIG. 38 aSIDAC or DIAC 436 is connected in series with the cable 352 Twooppositely oriented LEDs 438 and 440 are connected in parallel with theSIDAC or DIAC 436 through a resistor 442. The circuit of FIG. 39 issimilar to the circuit of FIG. 38 except that the SIDAC or DIAC 436 isreplaced with a second resistor 444. This is a very low cost option. Thecircuit of FIG. 40 is similar to that of FIG. 39 except that the secondresistor 444 is replaced with a bidirectional zener diode 446. Thiscircuit offers a good compromise between cost and brightness.

While we have described preferred embodiments of an improved sonde andline locator and improved methods of locating buried objects that emitan electromagnetic signal, they can be varied and modified in many ways.For example, the antenna arrays 44 and 46 could each have a ferrite coreinstead of an air core. Each coil in an array could be split intomultiple coils offset from the center line (axis of the elongate member34). Wiring these multiple coils in series would produce a signalsimilar to that of a single coil centered about the center line. Forexample, the multiple coils could be positioned on the flat surfaces ofa polyhedron such as an octahedron. Depth measuring capability is notessential so a second antenna array need not be used, or depth could besensed with only the lower array 44 with three mutually orthogonalantennas and a fourth antenna mounted on the elongate member 34 spacedfrom the array or within the housing 32. The features and attributes ofthe GUI including the selectable modes and the SEARCH and MAP viewscould be widely varied. Audible tones are not absolutely necessary.Conversely, audible tones could be used without any visual display.

Continuing with the description of various modifications to ourinvention, the physical shape of the housing 32 could be altered asneeded. The elongate member 32 that provides the antenna mast need notbe a hollow Aluminum or fiberglass tube but could be a solid member withany cross-section molded around the twisted pairs that connect thepre-amps 70 and 78 in the sensor balls 36 and 38 to the analog circuitboard 82 mounted in the housing 32 The arrangement and designation ofkeys on the keypad 106 could be widely varied. The signal from the upperantenna array 46 could be used when the system 30 is at or near one ofthe sonde poles to indicate the direction to the sonde. Either the firstembodiment or the second embodiment of our sonde and line locator couldincorporate a GPS receiver for downloading locating data and comparingthe same to stored municipal map data to ensure that well knownutilities are accounted for before commencing to locate a buried object.The housing 32 can incorporate a bubble level indicating device and aninternal two-axis (or more) accelerometer. The bubble level would helpthe operator locate buried pipes. The output of the accelerometer wouldhelp the system 30 correct the presented display information if theoperator did not hold the system 30 truly vertical. Further electronics,including the A/D, processors and gain and filtering blocks could becontained in or near the lower and upper sensor balls 36 and 38. Themarker chips 210 could be directly mounted to the housing 32.

The second embodiment of our sonde and line locator uses frequencydivision multiplexing (FDM) to simultaneously sense the differentelectromagnetic signals emitted by different utilities and to determinetheir different locations. However those skilled in the art willappreciate that a portable sonde and line locator incorporating thebasic concepts of our second embodiment could be designed to operatewith other well-known multiplexing schemes such as time divisionmultiple access (TDMA) or code division multiple access (CDMA).

The use of three coils represents a minimal solution for measuring themagnitude and direction of the magnetic field emanating from the buriedobject. There is no requirement that the coils be mutually orthogonal.Mathematically, the coils only need to be linearly independent. That is,the coils need to span the vector space of interest. By way of example,the first embodiment and the second embodiment of our sonde and linelocator could incorporate one antenna array that includes four or morenon-coplanar and non-co-axial antennas. In vector notation, threeorthogonal coils for a particularly simple basis set: {(1,0,0), (0,1,0),(0,0,1)}. An example of a non-orthogonal basis set would be {(1,0,0),(1,1,0), (1,1,1)}. A non-orthogonal basis set might be useful to satisfysome packaging constraint. A person skilled in the art would recognizethat orthogonality is not essential and it may be relaxed to meetphysical limitations on the configuration of the locator. The use offour or more coils in the first and second embodiments of our sonde andline locator provides a number of advantages. First, this configurationis robust against failures. It is generally easy to design the circuitryto recognize that one of the coils has failed and to drop back to an(n−1) mathematical solution. Second, the use of four or more coils makesthe locator less susceptible to very small scale perturbations in thefield. At least squares reduction to three mutually orthogonalcomponents of the field is possible by Gaussian elimination, SingularValue Decomposition or other standard methods. Third, the use of four ormore coils allows measurement of local gradients in the field. To dothis, a total of eight coils are needed. This is best illustrated byconsidering the first embodiment which uses a total of six coil, threecoils in each antenna array. More information would be desirable,namely, whether the vertical gradient is increased to the left or to thefront. The use of three additional coils to the front and threeadditional coils to the right yields a total of twelve coils to measurethese gradients, which results in an over-determined system. Theover-determined system can be solved in the least squares sense by thestandard methods to yield nine components:

*Bx/*x*By/*xa*Bz/*x [0134] *Bx/*y*By/*y*Bz/*y [0135] *Bx/*z*By/*z*Bz/*z

These nine components are not linearly independent because Maxwell'sequations require that the magnetic field has no divergence (del dotB=0) and there are only eight independent components and therefore aminimum of eight coils is required to fully resolve the local curvatureand magnitude of the magnetic field. Again, the positions andorientations of these coils do not have to be on a rectilinear set ofaxes but may be placed on the surface of a sphere, for example. Morethan eight coils may be reduced to the minimal set of components in aleast squares sense.

These and other modifications will be readily apparent to those skilledin the art. Therefore the protection afforded the present inventionshould only be limited in accordance with the scope of the followingclaims and their equivalents.

We claim:
 1. A method of locating a plurality of buried utilities,comprising: simultaneously receiving a plurality of electromagneticfield signals emitted by a corresponding plurality of buried utilitiesat a first antenna array of a magnetic field sensing locator, the firstantenna array including three nested substantially mutually orthogonalmagnetic field antennas; wherein the plurality of electromagnetic fieldsignals include at least a first magnetic field signal emitted by afirst buried utility and a second magnetic field signal emitted by asecond buried utility different from the first buried utility;simultaneously determining information associated with the plurality ofmagnetic fields in the locator; and providing a visual indication of thedetermined information associated with the magnetic fields emitted bythe plurality of buried utilities on a visual display the locator. 2.The method of claim 1, wherein the visual indication of the determinedinformation associated with the magnetic fields is provided as a graphicrepresentation on a graphic user interface (GUI).
 3. The method of claim1, wherein the visual indication includes an indication of distortion ofthe determined magnetic fields.
 4. The method of claim 1, wherein thevisual indication of the determined magnetic fields includes anindication of a tilt of the magnetic field relative to a referenceorientation.
 5. The method of claim 1, further comprising receiving GPSsignals in a GPS receiver disposed in the locator and storing positionalinformation determined from the GPS signals in a non-transitory memoryof the locator in conjunction with the determined magnetic fieldinformation.
 6. The method of claim 1, further comprising storingmunicipal map data associated with the buried utilities in the locatorfor presentation of the map information in conjunction with thedetermined magnetic field information and positional information.
 7. Amethod of locating a plurality of buried objects by sensing ones of aplurality of different electromagnetic signals emitted by ones of theplurality of objects, comprising the steps of: simultaneously sensingones of the plurality of magnetic field signals emitted fromcorresponding ones of the plurality of buried objects with an antennaarray including three concentrically positioned nested circular antennacoils, wherein the plurality of buried objects include at least a firstburied object, and a second buried object different from the firstburied object; simultaneously determining a plurality of differentlocations of the plurality of buried objects based on the sensed ones ofa plurality of magnetic field signals; and simultaneously providing adisplay including information associated with the ones of a plurality ofmagnetic fields and ones of the plurality of buried objects.
 8. Themethod of claim 7, wherein the displayed information includes a visualdisplay of magnetic field distortion.
 9. The method of claim 7, whereinthe displayed information includes a display of positional uncertaintyassociated with the buried objects.
 10. The method of claim 9, whereinthe display of position uncertainty includes a broken line displayassociated with the positional uncertainty.
 11. The method of claim 7,further comprising simultaneously providing an audible indicationassociated with the buried objects.
 12. The method of claim 11, whereinthe audible information includes synthesized voice information.
 13. Themethod of claim 12, wherein the synthesized voice information includesright or left directional information.
 14. A buried utility locator fordetecting a plurality of buried utilities, comprising: a first antennaarray including three or more substantially mutually orthogonal nestedcircular magnetic field antenna coils for receiving magnetic fieldsignals emitted from the plurality of buried utilities; a second antennaarray including three or more substantially mutually orthogonal nestedcircular magnetic field antenna coils for receiving magnetic fieldsignals emitted from the plurality of buried utilities, the secondantenna array positioned above the first antenna array when the locatoris in a vertical operating orientation; an electronic circuit havinginputs operatively coupled to outputs of the first and second antennaarrays, the electronic circuit configured to simultaneously determine aplurality of different locations of the plurality of buried utilitiesbased in part on the plurality of different magnetic field signalsreceived at the first antenna array and the plurality of differentmagnetic field signals received at the second antenna array, wherein theplurality of buried utilities include at least a first buried utility,and a second buried utility different from the first buried utility; anda display device configured to simultaneously provide a visual displayof the plurality of different buried utility locations.
 15. The locatorof claim 14, further comprising a GPS receiver for receiving GPS signalsand determining and storing the positional information in conjunctionwith the determined location information.
 16. The locator of claim 14,further comprising a circuit for providing an audible indication of theplurality of different locations.
 17. The locator of claim 14, furthercomprising a memory for storing municipal map data associated with theburied utilities for presentation of the map information in conjunctionwith the determined location information.